The invention provides a method for providing protection in an optical communication network against connection failures occurring in connections between nodes connected to each other by means of optical fibres in a ring structure.
Optical communication networks can connect nodes with each other by means of optical fibres in a ring structure. The ring architecture allows providing protection against line and device failures and against degradation in transmission performance. In such an optical communication network part of the transmission capacity can be dedicated to protection against failures and is therefore not normally utilized to convey data traffic. A relatively simple concept of such a ring structure is a 2-Fibre Optical-Channel Shared Protection Ring (2F-OCh-SPRing). In such a 2-Fibre bidirectional ring data traffic can travel in one direction in one fibre while data traffic in the opposite direction travels on the other fibre. In such a ring the functionality is similar to a pre-assigned restoration, but potentially faster since only the service end nodes need to perform a look-up and switch-over in case of a failure. For a large DWDM ring (Dense Wavelength Division Multiplexing) with meshed traffic pattern such a shared protection can offer increased ring capacity at comparatively low costs.
In U.S. Pat. No. 5,647,035 a ring network communication structure on an optical carrier and a reconfigurable node is described. A plurality of nodes is interconnected by means of connections that include at least a first and a second optical carrier such as an optical fibre. The transmission between the nodes occurs according to a WDM scheme utilizing a first wavelength for communication in one direction on a first carrier and a second wavelength for communication in the opposite direction on a second carrier. The second wavelength on the first carrier and the first wavelength on the second carrier are reserved for protection (protection channels). When a failure occurs on one of the connections nodes adjacent to the failed connection a node can reconfigure itself to ensure a continuation of the data communication on an alternative path of the ring, by utilizing the first wavelength on the second carrier and the second wavelength on the first carrier. In this conventional ring network multi-wavelength signals have to be managed since signal rerouting is localized at the nodes adjacent to the failure. The protection operations have to be performed on the entire set of wavelength of the multiplex section and the reconfigured nodes of the network must reroute all working channels that were previously sent on the damaged ring segment to their respective protection channels running onto the complementary ring arc. Consequently each node of this conventional network has to be equipped with optical switching tools for the complete set of wavelengths in the ring and a switch matrix is needed with a complexity which increases considerably with the increasing number of communication channels. Each client device needs for each logical traffic connection a transceiver/receiver pair and a corresponding switching matrix thus increasing the complexity significantly.
EP 1 075 105 A1 describes an autoprotected optical communication ring network having a first optical carrier configured to transport optical signals in a first direction and a second optical carrier configured to transport optical signals in a second direction that is opposite to the first direction. The plurality of nodes is connected along the first optical carrier and the second optical carrier to form bidirectional links. During a failure condition optical signals using a first wavelength on the second optical carrier and the second wavelength to the first optical carrier are exchanged. The rerouting operation is performed at the nodes that terminate the affected links only on the failed channels. However, each node of this optical communication network comprises a receiving/transmitting module consisting of a matrix arrangement of optical switches having a high complexity. The network of EP 1 075 105 A1 employs special switch matrias provided in the nodes which is therefore comprise a high technical complexity and are difficult to implement. Furthermore, this conventional network is not flexible.
Accordingly, it is an object of the present invention to provide a method far providing protection in an optical communication network against connection failures which can be implemented with a relative low technical complexity and which is flexible to changes in the network topology.